a) Field of the Invention
This invention relates to adjustment risers, and more especially to such risers which in use are matingly stacked to occupy a gap between a lower support structure and an upper frame assembly, especially in a manhole or catch basin. This invention further relates to an adjustment riser assembly; an assembly of a lower support structure an upper frame assembly and a stacked multiplicity of risers of the invention; and a method of inhibiting transmission of mechanical vibrations through an upper frame assembly to an adjacent lower support structure.
b) Description of Prior Art
Manholes which provide access to sewers or utility components, and catch basins for removal of rainwater, typically employ a lower support structure, for example, a concrete riser, a frame assembly typically of metal above the lower structure and a removable cover typically of metal to close and permit access to the lower structure and a conduit network communicating with the concrete riser.
A manhole typically has access steps to facilitate entry into the hole.
An adjustment riser is disposed between the lower structure, for example, a concrete riser and the frame assembly. The adjustment riser has two functions, first it occupies the gap between the lower structure and the frame assembly to complete the assembly of the manhole or catch basin, and secondly it absorbs mechanical vibrations developed above the frame assembly, such as by vehicles travelling over the metal cover when the hole is located in a road, and inhibits transmission of the mechanical vibrations to the lower structure, which mechanical vibrations would otherwise cause fractures or cracking in a concrete riser as the lower structure, shortening its life such that frequent repair or replacement becomes necessary.
In that the adjustment riser is to occupy a gap formed in part as a result of a lack of exactness in dimensions of components of the manhole or catch basin; and in part as a result of variations in requirements of different hole structures, such adjustment risers are fabricated in a variety of different thicknesses to accommodate different gap heights between the lower structure and the frame assembly in different holes. An adjustment riser of required thickness or a combination of thicknesses is then selected based on measured dimensions of the gap at a particular hole structure. Thick adjustment risers are heavy and difficult to handle.